This invention relates to a frame structure for a foundation unit such as a box spring, and more particularly to a frame which increases the strength of the foundation unit while at the same time reduces the complexity and cost of construction of the unit.
In the conventional frame for a foundation unit, the structure consists of a pair of flat side rails connected together at either end by an end rail. Normally, at least one center rail is utilized extending parallel to the side rails from one end rail to the other. A plurality of slats are placed flat across the frame from one side rail to the other, spaced at particular intervals from one end of the frame to the other. Normally, all frame sections are either stapled or nailed together.
This type of frame has several inherent disadvantages. Due to all slats being flat, there is some tendency for the slats to break in use. Since the slats are nailed or stapled together, the points of these fasteners may protrude through the side rails, contributing to torn mattress covers. Since the thickness of the frame normally is on the order of one and one-half inches, to create the normal seven inch box spring thickness, springs on the order of six inches in height must be utilized in the box spring, and thus a substantial amount of costly spring steel has to be used. Also, because the frame is either nailed or stapled together, any stress applied to the frame tends to loosen the framework, resulting in numerous rejected frames in the factory, and a number of unnecessary structural failures during use thereof.
Attempts to alleviate the above problems have previously been made. For example, U.S. Pat. No. 97,306 discloses a box spring structure which employs a plurality of rails placed on their edges between the frame of the box spring. Similarly, U.S. Pat. No. 2,773,271 discloses a frame structure in which a plurality of transverse frame members are placed on edge between a pair of longitudinal frame members. Each of these structures, although recognizing that an oblong member is stronger when oriented with its largest cross sectional dimension extending vertically, has failed to recognize the significantly greater strength of such a structure when the components are assembled in a particular manner.